In these years, the cutting machining pursues, in addition to high-speed, high-precision and high-efficiency machining, dry machining for addressing environmental issues. Further, with advances in industrial technology, some industries that frequently use difficult-to-cut materials and new materials for aircrafts, space development and nuclear power generation for example perform increasingly intense activities. It is thus expected that such materials will increase in variation in terms of quality and increase in amount. Accordingly, the cutting machining of these materials should address such increases of the materials. A number of surface-coated cutting tools that address the issue have been proposed and in actual use.
For example, Patent Document 1 discloses a hard-layer-coated tool and a hard-layer-coated member. Specifically, on a surface of such a hard base material as WC cemented carbide, cermet or high-speed steel of such a tool as cutting tool and wear-resistant tool, a hard coating layer that is an AlTiSi-based layer like (AlxTi1-x-ySiy) (NzC1-z) layer (where 0.05≦x≦0.75, 0.01≦y≦0.1, 0.6≦z≦1) is formed for the purpose of improving wear resistance and surface protection function.
Patent Document 2 discloses that at least one layer of nitride, carbonitride, oxynitride or oxycarbonitride containing an appropriate amount of Si and Ti as a main component and at least one layer of nitride, carbonitride, oxynitride or oxycarbonitride containing Ti and Al as a main component are alternately formed as coating layers. Here, in the fine structure of such a compound as TiSi-based compound, Si3N4 and Si are present as independent phases in the carbonitride, oxynitride or oxycarbonitride containing Ti as a main component. It is disclosed that the performance of a cutting tool having the above-described coating and used for dry and high-speed cutting machining is considerably improved. According to Patent Document 2, as for a conventional TiAlN film, while an alumina layer that is generated through surface oxidation occurring in a cutting process serves as an oxidation protection layer for inward diffusion of oxygen, the uppermost alumina layer is insufficient for addressing advances of the oxidation since the alumina layer is readily peeled off from the porous Ti oxide layer immediately below. It is disclosed that the TiSi-based coating of the invention described in Patent Document 2 itself is highly oxidation-resistant. In addition, since the composite oxide of Ti and Si that contains Si and is highly dense is formed at the uppermost surface, no porous Ti oxide layer that is a source of the problem of the conventional art is formed, the performance is improved.
Moreover, Patent Document 3 discloses that carbonitride or nitride of AlCrV can be used to generate coating quality for cutting tools that is higher in hardness and wear resistance as compared with the TiAlN film.
Patent Document 1: Japanese Patent No. 2793773
Patent Document 2: Japanese Patent No. 3347687
Patent Document 3: Japanese Patent Laying-Open No. 2003-34859